In order to adapt the steering wheel position to the seat position of the driver of a motor vehicle, adjustable steering columns are known in various configurations in the prior art. The steering wheel mounted at the rear end of the steering spindle in steering columns of this kind may be positioned by a length adjustment in the direction of the steering column's longitudinal axis in the longitudinal direction in the vehicle interior.
The lengthwise adjustability is realized in that the adjustment unit, consisting of an outer casing unit, or casing unit for short, and an inner casing tube, or casing tube for short, is mounted rotatably in the steering spindle, is telescopically adjustable in the direction of the longitudinal axis, i.e., in the longitudinal direction, and is securable in different lengthwise positions by means of a releasable clamping device, i.e., it is releasably securable. The clamping device, also known as a securing device, acts on the outer casing unit, which is held on the vehicle body, and in the opened state of the clamping device—also equivalently referred to as the release position or loosening position—a displacement of the inner casing tube in the outer casing unit is possible in order to adjust the steering wheel position and in the closed state—the fixing position or securing position—the inner casing tube is clamped in the outer casing unit and in normal driving operation the steering wheel position is fixed under the mechanical stresses to be expected.
A known effective measure for improving passenger safety during a vehicle collision, or so-called crash event, during which the driver impacts with high speed against the steering wheel, is to design the steering column to be collapsible even in the fixing position of the clamping device in the longitudinal direction when a force is exerted on the steering wheel in excess of a limit value only occurring in a crash event. In order to ensure a controlled braking of a body striking against the steering wheel, an energy absorption device is coupled in between the casing unit and the casing tube, which in normal operation are fixed together by the clamping device, but in a crash event are pushed together. This converts the introduced kinetic energy into plastic deformation of an energy absorption element, for example by tearing off a pull tab or bending an elongated bending element, such as a bending wire or a bending strip.
A steering column of this kind is described in DE 10 2008 034 807 B3. The clamping device described therein comprises a locking element which is supported on the outer casing unit in the longitudinal direction and which can be brought into force-locking and form-fitting engagement transversely to the longitudinal direction with a corresponding engagement part on the inner casing tube in the fixing position. In the release position, the locking element is lifted off from the engagement part and thereby released, so that the inner casing tube is displaceable relative to the casing unit for adjusting the steering wheel position in the longitudinal direction.
The engagement part is connected by an energy absorption device to the inner casing tube, which is not stressed in normal operation and forms a rigid connection between the outer casing unit and the inner casing tube. In a crash event, however, so great a force is introduced via the locking element into the engagement part that the holding force provided by the clamping device is overcome and the outer casing unit and the inner casing tube move relative to each other in the longitudinal direction, thereby deforming the energy absorption element and braking the movement.
Furthermore it is proposed in the mentioned DE 10 2008 034 807 B3 to design a controllable braking action of the energy absorption device so as to make provision in a crash event for whether the driver is wearing a seat belt or not, or to make an adjustment to parameters such as driver weight, distance from the steering wheel, and the like. Specifically for this purpose, at least two energy absorption elements should be provided, which can be activated when needed by being coupled in between the outer casing unit and the inner casing tube by being brought through the coupling device into mechanical operative connection between the engagement part and the inner casing tube. For the coupling to the energy absorption element, the engagement part comprises at least one first driver element, which can be brought into operative engagement with the first energy absorption element. Due to the design of the coupling device, at least one of the energy absorption elements can be coupled in between the inner casing tube and the engagement part, or at least one of the energy absorption elements can be coupled out. In this way, a switchable braking characteristic, or crash level, can be realized individually for the particular operating instance.
Another configuration of a switchable energy absorption device for a steering column is described in US 2015/0375773 A1. This likewise comprises two energy absorption elements, one of which can be coupled out in order to reduce the crash level by the coupling device from the flow of force between casing unit and inner casing tube. In this configuration, the driver element of the coupling device and the locking element directly engage with the energy absorption element, which may have a detrimental effect on the function.
The drawback to the energy absorption device already known from DE 10 2008 034 807 B3 is that a relatively large installation space is needed due to the arrangement of the energy absorption elements. The reliably switchable design of the coupling device is relatively costly.
Thus a need exists for a steering column with an improved switchable energy absorption device that ensures a high degree of functional reliability in a flexibly adaptable installation space.